The present invention relates to a calibration system of an adaptive array antenna; and, more particularly, to a calibration apparatus of the adaptive array antenna and a calibration method thereof, being capable of estimating and calibrating a transfer function corresponding to each channel without interfering with the other""s signal.
In general, an adaptive array antenna is employed in a wireless communication system because an antenna beam can be oriented to an aimed direction adaptively. Thus, the adaptive array antenna system provides a high antenna gain and an improved signal-to-noise ratio (SNR).
Furthermore, the adaptive array antenna which is embodied by a digital beamforming method for transmitting/receiving a plurality of signals simultaneously in a mobile communication base station, has an advantage of reducing an interference signal against the other signals because the antenna beam is formed independently for each signal.
The digital beamforming method controls an orientation angle and a sidelobe level of the array antenna by means of multiplying a transmitting/receiving signal and a beamforming weight together at a baseband. In this case, the transmitting/receiving signals from an array antenna system is assumed to be identical for an accurate the direction of arrival estimation and beamforming. Therefore, it is necessary to estimate and calibrate a transfer function of a transceiver exactly. Generally, the transfer function of the transceiver representing an amplitude and a phase is different from each other for each channel due to a characteristic of a radio frequency (RF) parts. Thus, it is necessary to perform a calibration step to measure and calibrate the transfer function periodically.
A conventional method for estimating the transfer function of the multi-channel transceiver uses the method to inject a calibration signal into each channel and to analyze the calibration signal transmitted through the transceiver.
The transfer function of each channel in an array antenna system is not only varied according to the change of the time but also changed by environmental conditions such as a temperature, a moisture and the like, whereby it is necessary to estimate and calibrate the transfer function periodically during the system""s working. However, there is a drawback that the calibration signal may interfere an original signal to transmit or be received through the adaptive array antenna when the calibration signal is injected into each channel.
To overcome the above drawback, there is announced a prior art which is disclosed in U.S. Pat. No. 5,530,449, entitled xe2x80x9cPhase Array Antenna Management System and Calibration Methodxe2x80x9d. In the disclosure, when a reference signal is formed in order to reduce the interference with the other user""s signal in the adaptive antenna system, an orthogonal-code modulated signal of a low voltage having a narrower bandwidth than a signal bandwidth, is used.
However, it is impossible to generate the orthogonal-code modulated signal uncorrelated with receiving a plurality of signals when the prior art is applied to an array receiving system in a code division multiple access (CDMA) mobile communication environment.
There is the other prior art disclosed in U.S. Pat. No. 5,248,982, entitled xe2x80x9cMethod and Apparatus for Calibration Phased Array Receiving Antennasxe2x80x9d. This prior art is related to the method for injecting two reference signals modulated to the orthogonal-code into each different transmission line. This method has an advantage that the effect of a signal line may be eliminated to apply the reference signal. However, the lengths of two reference signal input lines should be symmetric to each input terminal, and further it is difficult to reduce the interference with the other user""s signal.
It is, therefore, an object of the present invention to provide a calibration apparatus of an adaptive array antenna utilizing a calibration signal with low correlation to an array manifold as multiplying by a weight vector corresponding to a predetermined array response vector of the antenna, thereby reducing an interference signal.
It is another object of the present invention to provide a calibration method of an adaptive array antenna utilizing a calibration signal with low correlation to an array manifold as multiplying by a weight vector corresponding to a predetermined array response vector of the antenna, thereby reducing an interference signal.
It is further another object of the present invention to provide a computer-readable media for performing a calibration method of an adaptive array antenna utilizing a calibration signal with low correlation to an array manifold as multiplying by a weight vector corresponding to a predetermined array response vector of the antenna, thereby reducing an interference signal.
In accordance with an aspect of the present invention, there is provided a calibration apparatus of an adaptive array receiving antenna system having a plurality of array antennas, the calibration apparatus comprising: a calibration signal generating unit for generating a calibration signal of a baseband as the calibration signal of a radio frequency (RF) band; a calibration signal injection unit for injecting a calibration signal vector into an array receiving unit, wherein the calibration signal vector is produced by multiplying a divided signal by a predetermined weight corresponding to each channel, the divided signal being made by dividing the signal received from the calibration signal generating unit by total number of channels; a plurality of array receiving unit for adding the signal received from the calibration signal injection unit and the signal received by the array antenna devices, and for converting the signal of the RF band into the signal of the baseband; a calibration coefficient estimation unit for estimating a transfer function of each channel by correlating the signal received from the calibration signal generating unit with the signal received from the array receiving unit, and for finding out a calibration coefficient by using an estimated transfer function; and a calibration unit for eliminating an interference component by multiplying the signal received from the array receiving unit and the inverse of calibration coefficient together.
In accordance with another aspect of the present invention, there is provided a calibration apparatus of an adaptive array transmitting antenna system having a plurality of array antennas, the calibration apparatus comprising: a vector addition unit for adding each output of each beamforming unit; a calibration signal generating unit for generating a calibration signal to be injected into a channel for estimating a transfer function; a calibration signal injection unit for injecting a calibration signal vector added by the signal received from the vector addition unit, into a calibration unit; an array transmission unit for converting a digital data to an analog data, and for up-converting to an RF band; a coupling unit for interlocking a switch unit with the signal received from the array transmission unit; an exchange unit for selecting a path or a circuit of the signal received from the coupling unit; a calibration signal receiving unit for converting the signal received from the exchange unit from the RF band into the baseband; a calibration coefficient estimation unit for finding out a calibration coefficient by using that the transfer function of the array transmission unit is estimated sequentially through the calibration signal received from the calibration signal receiving unit; and a calibration unit for eliminating an interference signal by unit of multiplying the signal received from the calibration signal injection unit by an inverse of the transfer function estimated from the calibration coefficient estimation unit.
In accordance with further another aspect of the present invention, there is provided a calibration method of an adaptive array receiving antenna, the method comprising the steps of: a) generating a calibration signal in order to measure a transfer function of an array receiving unit; b) injecting a calibration signal vector into the array receiving unit, wherein the calibration signal vector is produced by multiplying a divided calibration signal and a predetermined weight vector corresponding to each channel together, the divided calibration signal being the calibration signal divided by total number of channels; c) finding out a calibration coefficient by using that the transfer function of each receiving channel is estimated by analyzing the signal injected from the array receiving unit; and d) generating a receive signal that an interference signal is eliminated, by multiplying the received signal of a baseband and the calibration coefficient together.
In accordance with further another aspect of the present invention, there is provided a calibration method of in an adaptive array transmitting antenna, the method comprising the steps of: a) generating a calibration signal in order to measure the transfer function of an array transmission unit; b) injecting a calibration signal vector into the array transmission unit, wherein the calibration signal vector is produced by multiplying the calibration signal and a predetermined weight vector corresponding to each channel together; c) finding out a calibration coefficient by using that the transfer function of each receiving channel is estimated by analyzing a down-converted signal after down-converting the signal injected from the array transmission unit; and d) generating a transmission signal that an interference signal is eliminated, by multiplying the transmission signal and the calibration coefficient together.
In accordance with further another aspect of the present invention, there is provided a computer-readable media storing software program instructions, the software program instructions disposed on a computer to perform a calibration method of an adaptive array receiving antenna, comprising the steps of: a) generating a calibration signal in order to measure a transfer function of an array receiving unit; b) injecting a calibration signal vector into the array receiving unit, wherein the calibration signal vector is produced by multiplying a divided calibration signal and a predetermined weight vector corresponding to each channel together, the divided calibration signal being the calibration signal divided by total number of channels; c) finding out a calibration coefficient by using that the transfer function of each receiving channel is estimated by analyzing the signal injected from the array receiving unit; and d) generating a receive signal that an interference signal is eliminated, by multiplying the received signal of baseband and the calibration coefficient together.
In accordance with still further another aspect of the present invention, there is provided a computer-readable media storing software program instructions, the software program instructions disposed on a computer to perform a calibration method of an adaptive array transmitting antenna, comprising the steps of: a) generating a calibration signal in order to measure the transfer function of an array transmission unit; b) injecting a calibration signal vector into the array transmission unit, wherein the calibration signal vector is produced by multiplying the calibration signal and a predetermined weight vector corresponding to each channel together; c) finding out a calibration coefficient by using that the transfer function of each receiving channel is estimated by analyzing a down-converted signal after down-converting the signal injected from the array transmission unit; and d) generating a transmission signal that an interference signal is eliminated, by multiplying the transmission signal and the calibration coefficient together.